The present invention concerns a system which allows, through digital processing, the SSB multiplexing and demultiplexing of a given number of base-band signals characterized by a frequency spectrum ranging from 0 to 4 kHz. Said base-band signals can be available as analog signals which, via a pre-processing network, are sampled at 8 kHz frequency and processed numerically; alternatively, the signals can be already coded in numerical form and time multiplexed on one or more transmission paths, i.e., 24 or 30 per path, more generally known as a 24 or 30 channel PCM stream. After an eventual preprocessing, the above mentioned base-band signals can be SSB multiplexed by digital processing. The latter operation supplies a signal which, by means of a digital to analog conversion and by means of subsequent modulations and filterings, can be allocated in the frequency range most suitable for transmission on frequency division systems (FDM systems).